[pure-silver] Re: Condenser envy
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 8 Apr 2008 21:30:37 -0700
----- Original Message -----
From: "Dennis Purdy" <dlp4777@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, April 08, 2008 6:00 PM
Subject: [pure-silver] Condenser envy
I am committed to my VC cold light head because my favorite
paper is VC and I don't want to use VC filters so I have an
Aristo VC head with florescent tubes in green and blue.
But I wish I could use a condenser head for the little
extra sharpness and contrast. It occurred to me that my
cold light head is the same diameter as the condenser
housing on my Beseler Condenser head. So if I attach my VC
cold light head to the top of the condenser housing doesn't
it become a VC condenser head? Would the light be
collimated the same as if I used the regular top to the
condenser head with the single light bulb? Am I missing
something here?
Dennis
This won't really result in higher contrast. The cold
light is a very diffuse source and even if its focused using
the condensers it will still be quite diffuse. In fact, most
condenser lamphouses are partially diffusing because they
use lamps with large diffuse surfaces. The result is a
source that is somewhat more collimated than a pure
diffusion head but far from a true collimated source using a
point source lamp. Actually, point sources are not too
practical for general use because they very much increase
the contrast of blemishes on the negative. The difference in
contrast between a diffusion and collimated source depends
on the photographic material. The effect is known as Callier
Effect. It depends on how much light is scattered by the
particals making up the image. For most B&W materials with
relatively fine grain silver crystals the effect is about
one paper grade increase from the true diffusion source to
the partially diffusing condenser source. For color film,
where the image is made up of very small, partially
transparent, dye particals the effect is almost nil. This is
one reason true point sources can be used for color work.
There is no practical difference in resolution or
acutance between a partially diffusing condenser and true
diffusion source despite the common myth. Diffusion sources
_do_ tend to reduce the effects of blemishes but only when
the same contrast of printing paper is used for comparison.
where the same negative is printed in both kinds of
enlargers, and the paper grade is adjusted to match, the
higher contrast required of the diffusion source will pick
the blemishes up again. To some degree this is not true
where the blemishes are in a different plane than the image,
for instance, on the support side. In that case the
diffusion source has some avantage in suppressing the
blemishes.
Point sources do increase resolution somewhat but that
may be partly because of the way they concentrat light in
the printing lens. A true condenser system working from a
point source is focused on the entrance pupil of the lens so
that the iris of the lens no longer functions. Exposure must
be controled in some other way than changing f/stop. Bessler
made a point source lamp for their enlargers for special
purpose use. I think they were mainly intended for printing
scientific negatives and for making very large color murals.
They may still be around on the used market.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
